One approach for placing underground piping, commonly called “mole drilling,” includes using an impact hammer to create an opening for a pipe. The impact hammer may be used inside a pipe or may tow the pipe along while drilling. The impact hammer is powered by a compressed air supplied by an air hose and impacts a drilling head (which may be, for instance, a metal such as steel or steel alloys) fastened to the end of the pipe. The impacting creates an opening in the ground and drives the pipe downward (when drilling vertically) or through (when drilling horizontally) into the ground. At the same time, the drilling head and/or impact hammer drags the pipe into the opening. When the target depth or length is reached, the air hose and impact hammer are pulled out of the pipe, leaving the drilling head in the ground at the end of the pipe. This pipe can now be used in various ways such as electrical, gas or water conduits, geothermal loops, etc.
However, when hammering the pipe into the ground, there can be significant friction forces applied to the outside of the pipe by the by the ground material around the pipe as shown in FIG. 1. In this example, ground material 100 causes friction forces (represented by arrows 110-117) which can slow the progression of pipe 120 and drill 130 through the ground material. This is especially true when the pipe is going into the water table as the wet soil compacts more around the pipe. In some cases, the ground friction forces can be so great, these forces can dramatically slow down the drilling process or even keep the pipe from advancing through the opening at all.